Chinese authorities clamped down on public demonstrations yesterday with a spate of detentions, mobile phone warnings and a heavy police presence to prevent a planned anti-Japanese protest.

The moves heightened suspicions that the communist government manipulated previous displays of public unrest to score diplomatic points.

Patriotic groups had called for fresh demonstrations on May 4 to mark the anti-Japanese protests in 1919 that became a symbol of resistance to foreign domination.

But the government warned that anyone who joined an unapproved march would face punishment. To further scare off would-be demonstrators, police closed Tiananmen Square yesterday morning and paramilitary troops waited on a side street near the Japanese embassy.

With the protests starting to threaten important trade links, the government appears to have decided to turn off the nationalist tap it opened last month.